*9*°l TAYLOR— SUCCESSION OF MOSSES 



457 



with P. Banksiana on the more mesophytic slopes, and eventually 

 may form a pure stand. During even the early pine stages we 

 may find a thick undergrowth of Juniperus communis, with or 

 without Arctostaphylos Uva-ursi. These may last until the oaks 

 begin to encroach upon the pines. Both the juniper and the 

 pines produce a dense shade throughout the year, and by shedding 

 needles form a layer of slowly decaying debris. Under the juniper, 

 particularly on north facing slopes, we find the most abundant 

 moss growth of the dune series. Beyond the juniper, where 

 Arctostaphylos is very thick, mosses may be present but are less 

 continuous. The bearberry is a plant of low trailing habit, and has 

 the effect of shutting out the relatively small amount of light 

 which penetrates through the dense covering of conifers, and renders 

 photosynthesis on the part of the mosses difficult. The most 

 abundant species of moss under the juniper is Thuidium delicatulum, 

 ordinarily considered very mesophytic. Here it forms a thick 

 continuous mat frequently excluding all seed plants as well as most 

 other moss species, and extending beyond the juniper in many 

 places. In this moss mat is a much smaller quantity of T. recogni- 

 tion, not mixed with the T. delicatulum but growing in similar 

 places and forming small but distinct portions of the mat. A 

 still smaller amount of T. abietinum appears occasionally. Scat- 

 tered through the Thuidium in very small quantities are two 

 other mesophytic species, Hylocomium triquetrum found at Paul, 

 and Collier gon Schreberi found at Miller. Both species are common 

 in the mesophytic forests farther north (2). About 15 other species 

 of mosses occur upon the pine dune. Some of these are found 

 occasionally under the juniper, but more often on the sand in open 

 places free from juniper, around the bases of trees, or on half-decayed 

 sticks. The most common of these are Ceratodon purpureus, 

 Dicranum scoparium, and Funaria hygrometrica, all of which are 

 species of fairly varied habitat. Much the same condition has 

 been found in all of the pine dunes studied. The mosses are most 

 abundant in total quantity and are most luxuriant on north 

 facing slopes, which in this region are also lakeward facing slopes. 

 A greater number of species occur here than elsewhere in the 

 dunes, unless it is in the transition oak-pine regions, where many 



